This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Neonatal rhesus macaques were inoculated orally with a mixture of three different envelope variants of single-cycle SIV and tissues of the alimentary canal were analyzed by PCR and in situ hybridization to identify the initial targets of mucosal transmission.